1. Field of the Invention
The present invention relates to a method of soldering a lead terminal to a substrate, and more particularly, it relates to a method of soldering a lead terminal, to be mounted on a substrate for holding terminal electrodes which are formed on both surfaces of the substrate, to the substrate.
2. Description of the Background Art
Generally known is a method of forming a single electronic component by preparing a substrate having at least one electronic component which is mounted on its substrate surface and soldering a lead terminal to the substrate. An exemplary method of manufacturing such an electronic component provided with a lead terminal is now described with reference to FIGS. 4 and 5.
First, a substrate 23 which are provided with terminal electrodes 21 and 22 in the vicinity of its first end surface 23a is prepared, The terminal electrode 21 is formed on a lower surface 23b of the substrate 23, while the terminal electrode 22 is formed on an upper surface 23c of the substrate 23 to be opposed to the terminal electrode 21 through the substrate 23.
Further, a plurality of chip-type electronic components 24a and 24b are temporarily fixed onto the lower surface 23b of the substrate 23. These chip-type electronic components 24a and 24b are temporarily fixed onto the lower surface 23b of the substrate 23 through an adhesive for temporary fixation.
On the other hand, a lead electronic component 25 is temporarily fixed onto the upper surface 23c of the substrate 23. The lead electronic component 25 has a plurality of lead terminals 26a and 26b, which are inserted in through holes (not shown) provided in the substrate 23.
Then, the substrate 23 is dipped in molten solder from the lower surface 23b, and thereafter drawn out from the same so that the molten solder adhering to the substrate 23 is solidified to solder the chip-type electronic components 24a and 24b to electrode lands (not shown) which are formed on the lower surface 23b of the substrate 23. Thus, the chip-type electronic components 24a and 24b are electrically connected to the electrode lands by solder 28, as shown in FIG. 5. The lead terminals 26a and 26b of the lead electronic component 25 are also electrically connected to electrode lands (not shown) which are formed on the lower surface 23b of the substrate 23 by solder 28.
Then, a lead terminal 27 having a pair of branch portions 27a and 27b is mounted on the end surface 23a of the substrate 23. The lead terminal 27 is provided with the branch portions 27a and 27b, which are formed on a forward end of an elongated body portion 27c in a bent-up manner to have spring properties themselves. Inner surfaces of the branch portions 27a and 27b are brought into contact with the terminal electrodes 21 and 22, for holding the substrate 23 therebetween. At this time, the lead terminal 27 is temporarily fixed to the substrate 23 due to the spring properties of the branch portions 27a and 27b.
Then, the substrate 23 shown in FIG. 5 is so turned as to downwardly direct the end surface 23a, dipped in molten solder and thereafter drawn out from the same, so that the molten solder adhering to the substrate 23 is solidified to solder the branch portions 27a and 27b to the terminal electrodes 21 and 22.
While the lead terminal 27 is soldered to the first end surface 23a of the substrate 25 in FIGS. 4 and 5, another lead terminal is also soldered to a second end surface, which is opposite to the end surface 23a of the substrate 23a. Thus, it is possible to obtain a composite electronic component having a pair of lead terminals, by bonding such a pair of lead terminals 27 to the substrate 23 provided with a plurality of electronic components 24a, 24b and 25.
In order to manufacture the aforementioned electronic component which is bonded with the lead terminal 27, (1) a step of soldering the electronic components 24a, 24b and 25 to the electrode lands provided on the substrate 23 and (2) a step of soldering the lead terminal 27 to the substrate 23 must be carried out independently of each other. Thus, a plurality of soldering steps must be carried out through complicated operations.
When the electronic components 24a and 24b are soldered onto the substrate 23, further, the molten solder may also adhere to the terminal electrode 21, to remain thereon in a solidified state. Consequently, the terminal electrode 21 may be increased in thickness by the solder adhering thereto such that it is difficult to hold the substrate 23 between the branch portions 27a and 27b. If the substrate 23 is forcibly inserted between the branch portions 27a and 27b, the spring properties of the branch portions 27a and 27b are deteriorated to reduce holding power for the substrate 23. In this case, therefore, it is necessary to remove the solder adhering onto the terminal electrode 21.